Dyslexics struggle to recognise voices: Study

London: It`s not just the numbers they
struggle with, people with dyslexia also find it hard to
recognise familiar voices, a new study has claimed.

The study, published in the journal Science, is the
first tentative evidence that small sounds in the human voice
that vary between people are difficult for dyslexics to hear.

The scientists said that many people may have some
degree of "voice blindness" and by studying it further would
help them better understand how the human brain has evolved to
recognise speech.

Because people who suffer from dyslexia are known to
struggle with phonemes when reading, a team at Massachusetts
Institute of Technology in the US wondered whether they might
also struggle hearing them in people`s voices.

To investigate, the MIT team grouped 30 people of
similar age, education and IQ into two camps: those with and
without a history of dyslexia.

The subjects were then given a training to learn to
associate 10 different voices -- half speaking English and
half speaking Chinese -- with 10 computer-generated avatars.
They were then later quizzed on how many of those
voices they could match to the avatars.

Non-dyslexics outperformed people with a history of
dyslexia by 40 per cent when listening to English. But this
advantage vanished when the groups were listening to Chinese.

Understanding the mechanics of voice recognition is
important, said the study`s lead author Tyler Perrachione,
because it allows a listener to pinpoint a familiar voice
above the hubbub of a crowded room.

Perrachione explained that very little is known about
voice blindness, which is formally called phonagnosia.

"In reality, phonagnosia is probably much more
common," he said, "but people who don`t recognise that voices
sound different may not even realise they lack the ability to
tell voices apart."

According to the researchers, humans rely on small
sounds called phonemes to tell one person from another.

As we first try to form the word dog, for example,
phonemes are the "duh"-"og"-"guh" sounds that our parents
prompt us to make.

But as we master the ability to read, we become less
reliant on recognising these sounds to read, and eventually
stop noticing them, the researchers said.

Despite ignoring them, however, phonemes remain
important for voice recognition. The tiny inflections in the
way people pronounce phonemes gives a listener cues to tell
one voice from another, they added.

Dorothy Bishop from the University of Oxford thinks
that this is because "when [they] are listening to Chinese, it
is a level playing field, because no one has learnt to hear
[Chinese] phonemes".

The researchers think that dyslexics don`t have as
comprehensive a phoneme sound library in their heads, and so
they struggle when they hear phonemes spoken by unfamiliar
voices because their "reference copy" isn`t as well-defined.